Solvents (and contaminants) are commonly removed from an SLA stream occurring, for example, as a result of industrial coating processes, through contact with an adsorbent such as activated carbon. When the adsorbent becomes saturated or nearly saturated with solvent, the adsorbent is regenerated using steam to heat up the adsorbent and displace the solvents and contaminants. The steam, solvents and contaminants leave the adsorber and are condensed. Two layers form if the solvents are insoluble in water. In this case, the solvents may be separated from the water by decantation. If the solvents are soluble in water, there will not be any separation, and the solvents must be separated from water by other means such as distillation.
Regeneration processes typically require that the water layer from decantation be further treated by air stripping or steam stripping to remove the dissolved solvents and other contaminants which remain in the water layer before the water is discharged to the sewer. In fact, government standards require the removal of dissolved solvents and contaminants from these effluent water streams prior to sewering these streams. Removal of solvents and contaminants from water exiting regeneration processes to an environmentally safe level where the water may be discharged to the sewer is both technically demanding and expensive. Treatment is particularly difficult and costly when the solvents and contaminants are soluble in water. In many such processes, a single air or stream stripping treatment is incapable of removing solvents and contaminants in quantities sufficient to permit the water to be safely discharged into the sewer.
U.S. Pat. No. 4,689,054 discloses a system wherein contaminant rich liquid phase functions from the stripping treatment are routed to an incinerator where they are consumed as fuel. A major disadvantage of direct incineration of liquid phase contaminants, however, is that expensive and difficult to attain licensing or permission is required before the liquid phase contaminants, which are viewed as hazardous waste, can be incinerated.
A need exists, therefore, for an environmentally safe solvent recovery system which is capable, in a single integrated treatment, of: 1) removing solvents and contaminants in quantities sufficient to permit water extracted from steam/solvent/contaminant mixtures obtained from regeneration of SLA adsorber vessels to be safely discharged into a sewer, 2) recovering the solvents in virtually pure form, and 3) disposing of the contaminants by an essentially non-polluting thermal oxidation procedure.